Seismic expansion joint covers for buildings in geographic regions that are prone to earthquakes are of special designs that allow for movements of the building elements on either side of the expansion gap that are very much greater than the movements that occur as a result of thermal expansion and contraction. In that regard, buildings currently being built in earthquake-prone regions are usually supported on isolators that attenuate the intensities of shocks imparted to the building structure but increase the durations and magnitudes of the swaying motions of the structure as it displaces and deforms when forces due to the earthquake are imposed on its foundation supports. When a building is composed of two or more adjacent independent structural units, each structural unit is subject to movements in an earthquake that are different in direction, frequency and magnitude. This is the case, indeed, regardless of whether the units are mounted on isolators or not. Adjacent structural units of a building are, accordingly, subject to large relative movements having components toward and away from each other (perpendicular to the gap)xe2x80x94x-axis movementsxe2x80x94and components parallel to the gapxe2x80x94y-axis movements. Because the connections between structural units at expansion joints (which might better be termed xe2x80x9cmotion-absorbing gapsxe2x80x9d) occur at the perimeters of the structural units, the movements include small but meaningful relative displacements vertically and angularly between floor portions on opposite sides of gaps due to the rocking of the floors at the perimeter of the structural unit about a fulcrum in the region of the bottom center of the structural unit.
U.S. Pat. No. 5,644,879 (Shreiner et al. Jul. 8, 1997), which is owned by the assignee of the present invention and is hereby incorporated herein by reference for all purposes, describes and shows a seismic expansion joint cover assembly that is adapted to span a gap between the floors of building sections on opposite sides of a motion-absorbing gap and that permits relative movements of the floors substantially horizontally toward and away from each other along an axis perpendicular to the gap (xe2x80x9cx-axis directionxe2x80x9d) and substantially horizontally relative to each other along an axis parallel to the gap (xe2x80x9cy-axis directionxe2x80x9d). The assembly includes a rectangular structural floor bridge panel that spans the gap in all relative positions of the floors. One end of the bridge panel is attached to the floor on one side of the gap (xe2x80x9cfloor Axe2x80x9d) for movement in the y-axis direction and against movement in the x-axis direction relative to floor A. The other end of the bridge panel is supported on the floor of the other building section (xe2x80x9cfloor Bxe2x80x9d) for movement in the x-axis direction and against movement in the y-axis direction relative to floor B.
In order for the upper surface of the seismic expansion joint cover to be substantially flush with the upper surfaces of floors A and B, floor B has a rectangular recess having a width in the y-axis direction substantially equalxe2x80x94with some clearancexe2x80x94to the y-axis width of the bridge panel and a length in the x-axis direction sufficient to permit excursions of floor A relative to floor B in the x-axis direction in an earthquake so that floor B supports the bridge panel in all positions of floors A and B relative to each other. In the normalxe2x80x94no earthquakexe2x80x94relative positions of floors A and B, the bridge panel occupies roughly half of the recess in floor B. When floors A and B are farthest apart in an earthquake, the bridge panel must occupy a small part of the recess, inasmuch as its floor B end must remain supported on floor B, but most of the recess is empty. When floors A and B are closest together in an earthquake, the bridge panel occupies most of the recess. Hence, a cover over the recess and the bridge panel provides a flush upper surface of the seismic expansion joint cover for supporting persons and other loads that move over the expansion gap in both a normal (no earthquake) condition and during an earthquake.
In particular, a cover plate frame is installed along the side and end edges of the recess and has side members closely adjacent the sides of the bridge panel and an end member spaced apart from the floor B end of the bridge panel far enough to permit the bridge panel to move toward the end of the recess of floor B relative to the floor bridge panel in the x-axis direction when the gap narrows. A first cover plate (xe2x80x9cpanel cover platexe2x80x9d) is supported by a portion of the bridge panel proximate to floor A. A second cover plate (xe2x80x9crecess cover platexe2x80x9d) is supported by the cover plate frame and by a portion of the bridge panel adjacent the floor B end. The panel cover plate and the recess cover plate have surfaces flush with each other and adjacent end edges slightly spaced apart from each other to permit normal movements of floors A and B due to thermal expansions and contractions of the building structures. The recess cover plate is resiliently attached to the cover plate frame such as to keep it in place horizontally while permitting it to lift from supported relation on the bridge panel and ride up onto and over a portion of the panel cover plate when the motion-absorbing gap narrows in an earthquake.
In its broadest aspects, the seismic expansion joint cover of the ""879 patent (referred to above) has a structural floor bridge panel that spans the motion-absorbing gap in all positions of floors A and B, a covered cavity that accepts the floor B end of the bridge panel in all positions of floors A and B, and two flush cover plates that provide a surface over which persons and objects move across the assembly. The recess cover plate is attached resiliently to the cover plate frame of the recess so that the recess cover plate can lift up and slide over the panel cover plate when the gap narrows
In order to avoid having to make the recess cover plate unduly thick and heavy, the ""879 patent proposes to provide one or more movable transverse beams to support the recess cover plate between the floor B end of the bridge panel and the end member of the cover plate frame. Each transverse beam extends between and is slidably supported by the side members of the cover plate frame. Control arms move the transverse beam toward and away from the end member of the cover frame upon and in a proportional relationship of one-half to movements of floor B relative to the bridge panel.
Despite having many advantages, some parts and assemblies of the seismic expansion joint cover of the ""879 patent are of relatively complicated and costly construction and somewhat time-consuming to install. One of the systems of the ""879 patent seismic expansion joint cover that has shortcomings of the foregoing nature is the moving beam assembly for supporting loads on the recess cover plate. The beams, linkages, and slide elements are expensive to make and install and add weight and complexity to the system. The weight produces relatively large inertial forces, which act not only on the components of the moving beam assembly but on the recess frame, the bridge panel, and the y-axis and x-axis supports for the bridge panel. Another undesirably complex arrangement is the resilient mounting of the recess cover plate on the recess frame (see FIG. 10 of the ""879 patent).
One object of the present invention is to provide a seismic expansion joint cover assembly for floors that is able to sustain a severe earthquake with little likelihood of damage to the components of the assembly or to the floor portions in which it is installed. Another object is to provide an expansion joint cover assembly that can be quickly and easily restored to its normal operating configuration after it has been disturbed by an earthquake. Still another object is to provide an expansion joint cover that has a flush, essentially smooth upper surface. It is also an object to provide a seismic expansion joint cover that can be fabricated in units that are easy to transport to a job site and to handle and install at the job site and to simplify some of the components and arrangements of the seismic expansion joint cover of the ""879 patent.
The foregoing objects are attained, in accordance with the present invention, by a seismic expansion joint cover assembly that is adapted to span a motion-absorbing gap between a floor A on one side of the gap and a floor B on the other side of the gap and that permits relative movements of floors A and B substantially horizontally toward and away from each other along an x-axis perpendicular to the gap and relative movements of floors A and B substantially horizontally relative to each other along a y-axis parallel to the gap. The seismic expansion joint cover includes a bridge panel, a retainer adapted to be affixed to floor A and supporting a first end of the bridge panel for movement in the y-axis direction and against movement in the x-axis direction relative to floor A, and a recess frame adapted to be affixed in a recess in floor B receiving a portion of the bridge panel in all positions of the bridge panel relative to floor B. A recess cover plate covers the recess, a portion of the recess cover plate adjacent the end nearer to the gap being supported in sliding relation on the bridge panel in all positions of the bridge panel relative to floor B and the end farther from the gap being joined to an end member of the recess frame remote from the gap. A collapsible/extensible honeycomb panel adapted to be received in the recess in floor B supports the portion of the recess cover plate that spans the recess between the second end of the bridge panel and the end member of the recess frame.
The honeycomb panel greatly simplifies the seismic expansion joint cover by eliminating the complicated moving beam and the associated linkages and slides of the seismic expansion joint cover of the ""879 patent. The honeycomb panel is 1) light in weight, thus reducing inertial forces throughout the moving structures and also making it easy to handle and install; 2) inexpensive and durable; and 3) provides excellent and structurally favorable support for the recess cover plate, in that it supports the recess cover plate uniformly over its area of engagement with the recess cover plate, rather than along a transverse band, thus making it possible to use a thinner plate.
In preferred embodiments, one end of the honeycomb panel is coupled to the bridge panel and the other end is secured against horizontal movements relative to the end member of the recess frame. The honeycomb panel may be coupled to the bridge panel by a first coupling member having many spaced-apart upstanding pins, each pin being received in a cell of the honeycomb panel. The other end of the honeycomb panel may be likewise secured against movement relative to the end member of the recess frame by a second coupling member having many spaced-apart upstanding pins, each pin being received in a cell of the honeycomb panel. The anchor pin members are simple and inexpensive, very easy to install, and considerably facilitate installation of the honeycomb panel.
It is desirable to have the underside of the honeycomb panel supported in sliding relation on a sheet of low-friction polymeric material installed on the floor of the recess of floor B. A suitable honeycomb panel is a honeycomb made of paperboard impregnated with a polymeric material. Honeycomb panels of other materials, such as aluminum and stainless steel can also be used.
Another aspect of the present invention relates to the way in which the recess cover panel is installed so that it normally is held down in supported relation on the bridge panel but is able to lift up and slide over a bridge panel cover plate when the energy-absorbing gap closes in an earthquake. In particular, the bridge panel has an upper surface formed by a sheet of a metal that attracts magnets, and the part of the recess cover plate that is supported on the bridge panel is held down on the metal sheet by magnetic strips affixed to the recess cover plate. The bridge panel cover plate is received on the portion of the bridge panel between the first end of the bridge panel and the end of the recess cover plate closer to floor A, the upper surfaces of the bridge panel cover plate and the recess cover plate normally being flush with each other. When the motion-absorbing gap closes in an earthquake, the magnetic strips release from the upper surface of the bridge panel, and the recess cover plate slides over the top of the bridge panel cover plate.
Among the advantages of the magnetic hold-down feature are the low sliding resistance of the magnets, which allows the recess cover plate to slide easily over the bridge panel when the gap widens, a desirably high hold-down force, low cost, and ease of installation. Moreover, the magnetic strips act as spacers between the recess cover plate and the bridge panel, thus avoiding metal to metal contact and reducing noise when persons and objects move across the cover plate. The magnitude of the hold-down force is readily established at a predetermined level by the total area of the magnetic strips. The bridge panel cover plate may also be held down on the bridge panel by magnetic strips affixed to the bridge panel cover plate, which provides the foregoing advantages and also permits the recess and panel cover plates to be of the same thickness and to be flush with each other.
A thermal expansion gap is provided between adjacent ends of the recess cover plate and bridge panel cover plate. The recess cover plate and bridge panel cover plate have nosings at the expansion gap configured to cause the recess cover plate to ride up over the upper surface of the bridge panel cover plate when the motion-absorbing gap closes in an earthquake. The nosings may include inter-engaging inclined surfaces that provide a camming action when they engage that lifts the end of recess cover plate at the expansion gap upwardly so that the bridge panel cover plate can slide under it. The nosing on the bridge panel cover plate has a top recess and the nosing on the recess cover plate has a tongue received in the top recess. The overlapping of the recess and tongue keeps the joint closed as the expansion gap narrows and widens due to thermal expansion and contraction.
To facilitate lifting of the recess cover plate, it is desirable to join the recess cover plate to the end frame member for resilient tilting movement. In an arrangement that is advantageous for its simplicity, minimal cost, and ease of installation, elastomeric washers are interposed between the recess cover plate and the end frame member.
For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings.